This invention is directed to the scanning devices, such as bar code scanners, and is more particularly concerned with an arrangement for reading optical symbols, e.g., small two-dimensional bar code symbols, such as may be used to identify the part number and serial number of an electronic module or the like. The invention is more particularly concerned with a device that is combined with an illuminator for shining light on the bar code symbol or other symbol to enhance the visibility and detectability of the readable matter that constitutes the symbol.
Recently, two dimension bar code systems have begun to be employed on small articles so that the article can be tracked thought a manufacturing process. For example, two dimensional bar code symbols are inscribed onto electronic parts, such as integrated circuits and printed circuit boards. Because of the high information density of the 2-D symbols, these can carry the part number, part serial number, and manufacturing history of the part, such as the place and date of manufacture, and all in a square that may be as small as three millimeters on a side. The symbols can be screen printed, ink jet printed, or laser-etched directly onto the top surface or the case of the device or part. However, in order to read the bar code easily on the first attempt, the illumination should impinge on the bar code symbol in a way that fully illuminates it but avoids flare from specular reflection. Unfortunately, current 2-D bar code scanners do not have any way of illuminating the bar code symbol at a low angle relative to the surface where it is inscribed, while the optic axis of the reader is oriented normal, i.e., substantially perpendicular to that surface.
Because of the small size of 2-D bar code symbols, the symbols can be difficult for the scanner to interpret where the lighting is uneven or if the contrast is too low. For example, Datamatrix(trademark) bar code, which has been selected as the EIA (Electronics Industry Association) standard for small parts marking, is in the form of a matrix of bars about three millimeters on a side. These are inscribed by laser etching onto the plastic or ceramic housing or package for the electronic module, or can be printed by an ink jet technique. In either event, if the lighting is such that the scanner picks up specular reflection, the bar code symbol will produce a wash out, and may take several attempts to obtain a valid reading. Consequently, current bar code scanners have had some difficulty in obtaining bar code data in industrial processes where the small parts are to be identified from these very small bar code symbols.
Accordingly, it is an object of this invention to provide an improved illumination arrangement for a optical symbol scanning device that avoids the drawbacks of the prior art.
It is another object to provide bar code scanner and low angle illuminator arrangement that permits rapid and accurate reading of small, high density bar code symbols.
It is a further object to provide a hand-held scanner and illuminator that permits a user to read and accurately decode a symbol on an article by contact with the article.
It is still a further object to provide an illuminator for a hand-held 2-D bar code scanner that can be incorporated into the working or distal face of the scanner and which provides low angle illumination at the proper contact location to illuminate the bar code symbol.
It is yet a further object to provide a fixed bar code scanner arrangement for identifying bar-coded parts that stream past, and which incorporates a low angle illuminator.
According to one aspect of this invention, a scanner assembly is configured for detecting and decoding a small-scale two-dimensional optical symbol, such as a 2-D bar code symbol, lying on a surface of an electronic module or other article. The scanner assembly can be a handheld contact device, or can be a fixed (i.e., machine-mounted) device that reads the bar code symbols on articles that flow past it. The scanner assembly includes a low-angle light delivery system that focuses the light from the scanner to the precise point where the light is needed, and at an angle at which problems from specular reflection are considerably reduced. This provides an improved contrast ratio and achieves quicker, more successful decoding. This is especially useful wherever very small bar code symbols are applied directly to the surface of the part, e.g., by ink-jet or screen printing, by peening, or by laser etching. These symbols characteristically have a low contrast ratio, and are not easy to read and decode where a conventional illumination system is used. However, the low angle light delivery system employed here optimizes the readability by concentrating the lighting on the target bar code symbol at a sharp angle. The readability can be further enhanced by magnifying the symbol. The angle at which the light strikes the surface of the article minimizes the xe2x80x9cwash outxe2x80x9d effect caused by shiny or irregular surfaces.
In one preferred embodiment, a portable, hand-held scanner device is employed, having a distal face on which is positioned a light-generating means for producing illumination to fall on the bar code symbol. This is oriented to shine distally. An objective lens or other focusing means focuses an image of the bar code symbol on an imager, e.g., a charge-coupled device (CCD) or a charge-injection device (CID) that is positioned proximally of the lens in the housing of the scanner device. Here, the focusing means defines an optic axis for the scanner. A low angle light delivery system is adapted to be mounted on the distal face of the scanner device. This may include a lens barrel having an optic axis aligned with the optic axis of said scanning device, and carrying a lens, e.g., at its distal end. The lens may be omitted from the lens barrel in some designs. There are at least one light pipe, and preferably a pair of light pipes sandwiching the lens barrel between them. The light pipes have a flat proximal face to receive illumination from the light-generating means and an angulated distal face for projecting the illumination at a sharp angle relative to the optic axis. Here, the scanner arrangement is configured as a contact scanner and is to be positioned with the distal tip of the light pipe or pipes against the bar code symbol. In that position, the light from light delivery system impinges on the bar code symbol at a low angle relative to the surface of the article, while the optic axis of the scanner is substantially normal to the surface of the article.
In another preferred embodiment, the bar code scanner assembly can be configured for fixed scanning applications. In such case, the lens and imager are contained in a housing that is mounted in a fixed position, with associated electronics also carried withing the housing. The lens and imager define an optic axis. In this embodiment, the light delivery system involves an array of LEDs, laser diodes, or the like mounted in the housing at a position offset from the optic axis, angled so that the light crosses the optic axis at a sharp angle, e.g., 60-75 degrees. The parts to be scanned can pass beneath the scanner assembly on a plane at which the image of the bar code symbols will be in focus. When the bar code symbols are positioned at the optic axis of the scanner device, the illumination impinges the symbols at a low angle, e.g., 15-30 degrees, for optimal reading and decoding.
Illumination is not limited only to light in the visible spectrum, but may be infrared or other wavelengths.
The above and many other objects, features, and advantages of this invention will present themselves to persons skilled in this art from the ensuing description of preferred embodiments of this invention, as described with reference to the accompanying Drawing.